The present invention relates to a display, and especially a color display, which comprises an organic electroluminescent light emitting device (which will hereinafter be often called an organic EL device for short) using an organic compound.
In recent years, organic EL light emitting devices have been under intensive investigation. One typical light emitting device includes a glass substrate and a transparent electrode or anode of tin-doped indium oxide (ITO) or the like formed on the substrate. A thin film serving as a hole transporting layer is formed on the anode by evaporating a hole transporting material such as tetraphenyldiamine (TPD). A light emitting layer of a fluorescent material such as an aluminum quinolinol complex (Alq.sup.3) is deposited on the hole transporting layer. An electrode or cathode is formed thereon from a metal having a low work function such as magnesium. Such organic EL devices attract attentions because they can achieve a very high luminance ranging from 100 to 1,000 cd/m.sup.2 with a drive voltage of approximately 10 volts.
Displays constructed using such an organic EL device may potentially have various applications, and its application to color displays in particular is an important subject. When a light emitting device is applied as a color display, for instance, it is a common procedure to vary the color of light emitted from the light emitting device or use color filters to obtain the three primary colors, blue, green and red. One known approach to varying the color of light emitted from a light emitting device itself is embodied by a color light emitting device comprising a cathode formed of an Ag.Mg thin film and an anode formed of ITO as typically set forth in SID 96 DIGEST.185 14.2: Novel Transparent Organic Electro-luminescent Devices G. Gu, V. BBulovic, P. E. Burrows, S. RForrest, M. E. Tompson. However, this color light emitting device (heterostructure organic light emitting device) has a multilayer structure comprising light emitting layers (Red ETL, Green ETL and Blue ETL) corresponding to the three primary colors, R, G and B, respectively. One problem with this device is that its structure becomes complicated with a production cost increase because a cathode and an anode must be provided for each light emitting layer. Another problem is that the color balance is disturbed with time due to a service life difference between the three primary colors.
Even with a color display constructed using a single light emitting device in combination with color filters, on the other hand, it is difficult to achieve the emission of white light because an organic EL device has a limited light emission wavelength range with the uneven distribution of its center wavelength. The sole use of color filters leads to a deficiency of light sources for some wavelengths.